1. Field of the Invention
The present invention relates to a reproduction apparatus for printing a digital image comprising a control unit and a print engine, where the digital image is constituted of pixels, each pixel having assigned a pixel value; the print engine comprising print elements for ejecting an amount of marking material on a receiving material according to a pixel value, the reproduction apparatus further comprising a detector for detecting or predicting a failing print element.
2. Description of Background Art
Reproduction apparatuses are known which are able to print jobs arriving at the reproduction apparatus via a network or an analogue document via a scanner being part of the reproduction apparatus. Such a job may contain an image or a text or both an image and a text in black-and-white format or in color format. The job entry in the reproduction apparatus may be controlled by a controller, for example a computer, a control unit or a processor inside the reproduction apparatus. Also the controller may convert image and text data into commands for the print unit to let the print elements eject marking material at the right spot and the right time on the receiving material. The memory of the reproduction apparatus comprises a work memory part for loading and modifying images and a save memory for saving images.
However, print elements may fail when they become clogged or misdirecting.
Detectors are known, which can detect such a failing print element during printing or which can predict a high probability that a print element will fail within a short time. The visibility of a failing print element on the receiving material depends on the print strategy. In a multi-pass approach, a failing print element appears typically less visible than in a single pass approach. In a multi-pass approach each pixel line is addressed by multiple print elements and a failing print element may be compensated by filling in with another print element, for example in a later pass. However, such a print element failing correction for a multi-pass approach will not be possible in a single pass approach, where each pixel line is addressed by only one print element.
In a single pass approach, the failing print element immediately produces a light stripe in the print image on the receiving material and there is no chance to fill in this location later by means of another print element.
As soon as a failing print element is detected, while using a multi-pass strategy or a single pass strategy, other print elements than the failing print element might compensate for missing ejections of drops by the failing print element. Based on the information of the digital image to be printed, the locations on the receiving material to be printed upon by the failing print elements are determined and the correcting print data of the other print elements is determined during printing. A disadvantage is that during printing, a lot of image processing has to be done, which leads to a delay in correcting the failing print element. During this delay, the printing by the reproduction apparatus goes on, resulting in printed images with print artifacts due to the failing print element. This leads also to a loss of productivity of the reproduction apparatus.